Inorg. Chem. 2008, 47, 5386-5393
Macrocyclic Nickel(II) Complexes Coligated by Hydrosulfide and Hexasulfide Ions: Syntheses, Structures, and Magnetic Properties of [NiII2L(µ-SH)]+ and [{LNiII2}2(µ-S6)]2+ Vasile Lozan and Berthold Kersting* Institut fu¨r Anorganische Chemie, UniVersita¨t Leipzig, Johannisallee 29, 04103 Leipzig, Germany Received February 22, 2008
The borohydride complex [NiII2L(µ-BH4)]+ (3) where L2- represents a sterically demanding hexaaza-dithiophenolate ligand reacts rapidly with elemental sulfur in acetonitrile at ambient temperature to produce the cationic complexes [NiII2L(µ-SH)]+ (4) and [{NiII2L}2(µ-S6)]2+ (6). Both complexes were isolated as ClO4- or BPh4- salts and characterized by IR and UV/vis spectroscopy and X-ray crystallography. Complex 4 (also accessible from [NiII2L(ClO4)]+ (5) and Na2S · 9H2O) features an unprecedented N3NiII(µ-SR)2(µ-SH)NiIIN3 core structure, the hydrosulfide ligand being deeply buried in the binding-cavity of the bowl-shaped [NiII2L]2+ complex. In 6, a helical S62- chain, with a structure reminiscent to that of plastic sulfur, is almost completely encapsulated by two [NiII2L]2+ subunits. In contrast to other triply sulfur-bridged N3NiII(SR)3NiIIN3 structures whose ground states are typically of S ) 0, 4 reveals an S ) 2 ground-state which is attained by a ferromagnetic exchange interaction between the two Ni(II) (S ) 1) ions (J ) 18 cm-1, H ) -2JS1S2). Intradimer ferromagnetic exchange interactions are also present in 6 (J ) 23 cm-1). A qualitative explanation for this difference is offered.
Introduction The study of the coordination chemistry of classical coordination compounds with deep binding cavities is an active research area.1,2 Motivations in this area are diverse and include molecular recognition of neutral or charged guest molecules,3,4 stabilization of unusual substrate coordination modes, isolation of reactive species,5 promotion of reactions within their interiors,6–11 and construction of more effective enzyme active site mimetics,12 to name but a few. Various types of supporting ligands for such complexes have been * To whom correspondence should be addressed. E-mail:
[email protected]. (1) Canary, J. W.; Gibb, B. C. Prog. Inorg. Chem. 1997, 45, 1–83. (2) Wieser, C.; Dieleman, C. B.; Matt, D. Coord. Chem. ReV. 1997, 165, 93–161. (3) Poorters, L.; Armspach, D.; Matt, D.; Toupet, L.; Jones, P. G. Angew. Chem. 2007, 119, 2717–2719; Angew. Chem., Int. Ed. 2007, 46, 2663-2665. (4) Hammes, B. S.; Ramos-Maldonado, D.; Yap, G. P. A.; Liable-Sands, L.; Rheingold, A. L.; Young, V. G., Jr.; Borovik, A. S Inorg. Chem. 1997, 36, 3210–3211. (5) Rohde, J.-U.; In, J.-H.; Lee, M. H.; Brennessel, W. W.; Bukowski, M. R.; Stubna, A.; Mu¨nck, E.; Nam, W.; Que, L, Jr. Science 2003, 299, 1037–1039. (6) Reetz, M. T.; Waldvogel, S. R. Angew. Chem. 1997, 109, 870–873; Angew. Chem., Int. Ed. Engl. 1997, 36, 865-867. (7) Ooi, T.; Kondo, Y.; Maruoka, K. Angew. Chem. 1998, 110, 3213– 3215; Angew. Chem., Int. Ed. 1998, 37, 3039-3041.
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developed. Most of them represent mononucleating systems derived from cyclodextrines,6 calixarenes,13 Schiff-base/ calixarene hybrids, and some highly functionalized tripod ligands.14–18 Much less is known of ligand systems that encapsulate polynuclear core structures, and the chemistry of such systems is not well explored.19–21 (8) Yoshizawa, M.; Takeyama, Y.; Kusukawa, T.; Fujita, M. Angew. Chem. 2002, 114, 1403–1405; Angew. Chem., Int. Ed. 2002, 41, 1347-1349. (9) Engeldinger, E.; Armspach, D.; Matt, D. Angew. Chem. 2001, 113, 2594–2597; Angew. Chem. Int Ed. 2001, 40, 2526-2529. (10) Slagt, V. F.; Reek, J. N. H.; Kramer, P. C. J.; van Leeuwen, P. W. N. M. Angew. Chem. 2001, 113, 4401–4404; Angew. Chem., Int. Ed. 2001, 40, 4271-4274. (11) Yandulov, D. V.; Schrock, R. R. Science 2003, 301, 76–83. (12) Rondelez, Y.; Bertho, G.; Reinaud, O. Angew. Chem. 2002, 114, 1086– 1088; Angew. Chem., Int. Ed. 2002, 41, 1044-1046. (13) Cameron, B. R.; Loeb, S. J.; Yap, G. P. A. Inorg. Chem. 1997, 36, 5498–5504. (14) Kitayima, N.; Tolman, W. B. Prog. Inorg. Chem. 1995, 43, 419–531. (15) Trofimenko, S. Scorpionates: The Coordination Chemistry of Polypyrazolylborate Ligands; Imperial College Press: London U.K., 1999. (16) MacBeth, C. E.; Golombek, A. P.; Young, V. G., Jr.; Yang, C.; Kuczera, K.; Hendrich, M. P.; Borovik, A. S. Science 2000, 289, 938– 941. (17) Cho, J.; Yap, G. P. A.; Riordan, C. G. Inorg. Chem. 2007, 46, 11308– 11315. (18) Desrochers, P. J.; Cutts, R. W.; Rice, P. K.; Golden, M. L.; Graham, J. B.; Barclay, T. M.; Cordes, A. W. Inorg. Chem. 1999, 38, 5690– 5694.
10.1021/ic8003432 CCC: $40.75
2008 American Chemical Society Published on Web 05/20/2008
Hydrosulfide and Hexasulfide Ions
ClO4-, ReO4-, CrO42-, MoO42-, WO42-,35 alkylcarbonates (ROCO2-),25,20 alkyl carbamates (RNCO2-),36 and some five-membered N heterocycles.37 Recently, we have reported the stabilization of quite reactive and unusual species such as [Ni2L(BH4)]+,38 and [CoII2L(MoO3OMe)].39 As part of this program, we sought to extend our exploration to the syntheses of nickel complexes incorporating hydrosulfide (HS-) coligands. Our motivation was 5-fold: (a) hydrosulfide complexes of labile transition-metal ions are rather scarce,40–44 (b) the hydrosulfide ion is a biologically relevant molecule,45 (c) nickel sulfur bonding is of importance in bioinorganic46–48 and biomimetic chemistry,49–57 (d) the chemistry of SH- containing complexes is of relevance to metal sulfide hydrosulfurization catalysts,58–60 and (e) coligands with “soft” donor atoms have not been incorporated in the binding pocket of the [MII2L]n+ complexes. A general problem associated with the preparation of hydrosulfide complexes is further aggregation which leads to the formation of polynuclear sulfido complexes and eventually to insoluble metal sulfides. Herein we demonstrate that the sterically demanding supporting ligand L2- enables the isolation and characterization of the stable hydrosulfide
Figure 1. Cationic [MII2L(µ-L′)]+ complexes supported by L2- (L′ ) coligand), and schematic representation of their structures.
The coordination chemistry of binucleating hexaazadithiophenolate macrocycles has been reviewed.22,23 The N6S2 ligand H2L in its doubly deprotonated form supports the formation of dinuclear complexes of composition [MII2L(µL′)]n+ (M ) Mn, Fe, Co, Ni, Zn) whose two possible ligand conformations24,25 are reminiscent of the “partial cone” (type A) and “cone” conformations (type B) of the calixarenes (Figure 1).26 The coligands (L′) include Cl-,27 OH-,28 NO2-, NO3-, N3-, N2H4,29 carboxylates,30–34 HCO3-, H2PO4-,30 (19) Herold, S.; Lippard, S. J. J. Am. Chem. Soc. 1997, 119, 145–156. He, C.; Lippard, S. J. J. Am. Chem. Soc. 1998, 120, 105–113. (20) Hagadorn, J. R.; Que, L, Jr.; Tolman, W. B. J. Am. Chem. Soc. 1998, 120, 13531–13532. (21) Du Bois, J.; Mizoguchi, T. J.; Lippard, S. J. Coord. Chem. ReV. 2000, 200-202, 443–485. (22) Marr, A. C.; Spencer, D. J. E.; Schro¨der, M. Coord. Chem. ReV. 2001, 219-221, 1055–1074. (23) Brooker, S. Coord. Chem. ReV. 2001, 222, 33–56. (24) Kersting, B. Z. Anorg. Allg. Chem. 2004, 630, 765–780. (25) Gressenbuch, M.; Lozan, V.; Steinfeld, G.; Kersting, B. Eur. J. Inorg. Chem. 2005, 2223–2234. (26) Gutsche, C. D. Calixarenes; Royal Society of Chemistry: Cambridge, U.K., 1989. (27) Kersting, B.; Steinfeld, G. Chem. Commun. 2001, 1376–1377. (28) Klingele, M. H.; Steinfeld, G.; Kersting, B. Z. Naturforsch. 2001, 56b, 901–907. (29) Hausmann, J.; Klingele, M. H.; Lozan, V.; Steinfeld, G.; Siebert, D.; Journaux, Y.; Girerd, J.-J.; Kersting, B. Chem.sEur. J. 2004, 10, 1716–1728. (30) Kersting, B. Angew. Chem. 2001, 113, 4109–4112; Angew. Chem., Int. Ed. 2001, 40, 3987-3990. (31) Kersting, B.; Steinfeld, G. Inorg. Chem. 2002, 41, 1140–1150.
(32) Steinfeld, G.; Lozan, V.; Kersting, B. Angew. Chem. 2003, 115, 2363– 2365; Angew. Chem., Int. Ed. 2003, 42, 2261-2263. (33) Lozan, V.; Buchholz, A.; Plass, W.; Kersting, B Chem.sEur. J. 2007, 13, 7305–7316. (34) Klingele, J.; Klingele, M. H.; Baars, O.; Lozan, V.; Buchholz, A.; Leibeling, G.; Plass, W.; Meyer, F.; Kersting, B. Eur. J. Inorg. Chem. 2007, 5277–5285. (35) Lozan, V.; Kersting, B. Eur. J. Inorg. Chem. 2007, 1436–1443. (36) Lozan, V.; Holldor, J.; Kersting, B. Inorg. Chim. Acta, in press. (37) Lozan, V.; Voitekhovich, S. V.; Gaponik, P. N.; Ivashkevich, O. A.; Kersting, B. Z. Naturforsch., in press. (38) Journaux, Y.; Hausmann, J.; Lozan, V.; Kersting, B. Chem. Commun. 2006, 83–84. (39) Lozan, V.; Kersting, B. Inorg. Chem. 2006, 45, 5630–5634. (40) Kuwata, S.; Hidai, M. Coord. Chem. ReV. 2001, 213, 211–305. (41) Huang, S. D.; Lai, C. P.; Barnes, C. L. Angew. Chem. 1997, 109, 1961–1964; Angew. Chem., Int. Ed. Engl. 1997, 36, 1854-1856. (42) Howard, W. A.; Parkin, G. Organometallics 1993, 12, 2363–2366. (43) Rombach, M.; Vahrenkamp, H. Inorg. Chem. 2001, 40, 6144–6150. (44) Zhang, Y.; Zuo, J.-L.; Zhou, H.-C.; Holm, R. H. J. Am. Chem. Soc. 2002, 124, 14292–14293. (45) Howard, J. B.; Rees, D. C. Chem. ReV. 1996, 96, 2965–2982. (46) Fontecilla-Camps, J. C.; Volbeda, A.; Cavazza, C.; Nicolet, Y. Chem. ReV. 2007, 107, 4273–4303. (47) Doukov, T. I.; Iverson, T. M.; Seravalli, J.; Ragsdale, S. W.; Drennan, C. L. Science 2002, 298, 567–572. (48) Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C. Science 1998, 282, 1853–1858. (49) Swenson, D.; Baenziger, N. C.; Coucouvanis, D. J. Am. Chem. Soc. 1978, 100, 1932–1934. (50) Stavropoulos, P.; Carrie, M.; Muetterties, M. C.; Holm, R. H. J. Am. Chem. Soc. 1990, 112, 5385–5387. (51) Wilker, J. J.; Gelasco, A.; Pressler, M. A.; Day, R. O.; Maroney, M. J. J. Am. Chem. Soc. 1991, 113, 6342–6343. (52) Marganian, C. A.; Vazir, H.; Baidya, N.; Olmstead, M. M.; Mascharak, P. K. J. Am. Chem. Soc. 1995, 117, 1584–1594. (53) Grapperhaus, C. A.; Darensbourg, M. Y. Acc. Chem. Res. 1998, 31, 451–459. (54) Liu, X.; Ibrahim, S. K.; Tard, C.; Pickett, C. J. Coord. Chem. ReV. 2005, 249, 1641–1652. (55) Bouwman, E.; Reedijk, J. Coord. Chem. ReV. 2005, 249, 1555–1581. (56) Mealli, C.; Rauchfuss, T. B. Angew. Chem. 2007, 119, 9100–9102; Angew. Chem. 2007, 46, 8942-8944. (57) Eckert, N. A.; Dougherty, W. G.; Yap, G. P. A.; Riordan, C. G. J. Am. Chem. Soc. 2007, 129, 9286–9287. (58) Gaffney, T. R.; Ibers, J. A. Inorg. Chem. 1982, 21, 2857–2859. (59) Rauchfuss, T. B.; Ruffing, C. J. Organometallics 1982, 1, 400–401. (60) Mueting, A. M.; Boyle, P.; Pignolet, L. H. Inorg. Chem. 1984, 23, 44–48.
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complex [Ni2L(µ-SH)] (4). A tetranuclear nickel(II) complex [{Ni2L}2(µ-S6)]2+ (6) bearing a helical µ4-hexasulfide ligand is also described as are results of temperaturedependent magnetic susceptibility measurements on 4 · BPh4 and 6 · (BPh4)2. Experimental Section General Methods and Instrumentation. All manipulations were carried out using standard Schlenk-line (Ar) techniques. Reagent grade solvents were used throughout. Melting points were determined in open glass capillaries and are uncorrected. Infrared spectra were recorded on a Bruker TENSOR 27 FT-IR-spectrometer. UV/ vis spectra of solutions were measured on a Jasco 670 UV/vis/ near spectrometer in the range 250-1600 nm at ambient temperatures. Elemental analyses were carried out with a VARIO EL elemental analyzer. The temperature-dependent magnetic susceptibility measurements were carried out on a SQUID magnetometer (MPMS 7XL Quantum Design) over the temperature range 2-300 K in an external magnetic field of 0.5 T. The experimentally determined susceptibility data were corrected for the underlying diamagnetism using Pascal’s constants. Starting Materials. The complexes [Ni2L(Cl)]ClO4 (1 · ClO4),27 [Ni2L(BH4)]ClO4 (3 · ClO4),38 and [Ni2L(ClO4)]ClO4 (5 · ClO4)35 were prepared according to literature procedures. All other reagents were obtained from standard commercial sources and used without further purifications. CAUTION! Perchlorate salts are potentially explosiVe and should therefore be prepared only in small quantities and handled with appropriate care. [Ni2L(µ-SH)]BPh4 (4 · BPh4). Method A. To a solution of [Ni2L(BH4)]ClO4 (90 mg, 0.10 mmol) in acetonitrile (30 mL) was added a solution of elemental sulfur (3.2 mg, 0.10 mmol) in acetonitrile (10 mL), to produce a rapid color change from green to yellow-brown. The mixture was stirred for 1 h, NaBPh4 (342 mg, 10.0 mmol) in MeOH (10 mL) was added, and the resulting solution concentrated to about half of its original volume. After standing for 2 days brown-yellow crystals of [Ni2L(SH)]BPh4 were collected by filtration. Yield: 80 mg (70%). M.p.: 244-245 °C. IR (KBr disk): ν ) 2552 (vw, ν(SH)), 734 (s, ν(BPh4-)), 705 cm-1 (s, ν(BPh4-)). UV/vis(CH3CN): λmax/nm (ε/M-1 cm-1): 274 (16921), 304 (sh, 13080), 330 (10158), 662 (34), 1178 (53). ESI-MS (CH3CN): m/z (rel. intensity) ) 392.16 (60, [Ni2L]2+), 412.68 (100, [Ni2L(NCMe)]2+). Elemental analysis calcd (%) for C62H85BN6Ni2S3 (1138.77): C 65.39, H 7.52, N 7.38, S 8.45; found: C 65.20, H 7.28, N 7.62, S 8.22. Method B. A solution of Na2S · 9H2O (48 mg, 0.200 mmol) in methanol (5) was added to a green solution of [Ni2L(ClO4)]ClO4 (99 mg, 0.100 mmol) in acetonitrile (40 mL). The mixture was stirred 3 h during which it became yellow-brown. A solution of LiClO4 · 3H2O (160 mg, 1.00 mmol) was added and stirring was continued for another 2 h. The resulting precipitate of 4 · ClO4 was filtered, washed with 2 mL of cold methanol and dried under vacuum. Yield: 71 mg % (77%). 303-304 °C (decomp). IR (KBr disk): ν ) 2552 (vw, ν(SH)), 1094 (vs, ν3(ClO4-)), 627 cm-1 (s, ν4(ClO4-)). UV/vis(CH3CN): λmax/nm (ε/M-1 cm-1): 274 (16010), 301 (sh, 14138), 331 (10080), 663 (32), 1175 (49). Adding NaBPh4 (342 mg, 1.00 mmol) to a solution of 4 · ClO4 (92 mg, 0.10 mmol) in MeOH (50 mL) provides, after filtration, recrystallization, and drying under vacuum, 96 mg (84%) of 4 · BPh4. The analytical data of this material are identical to that of the compound prepared by method A.
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Table 1. Crystallographic Data for 4 · BPh4 · MeOH · 2H2O and 6 · (BPh4)2 · 5MeCN 4 · BPh4 · MeOH · 2H2O
6 · (BPh4)2 · 5MeCN
C134H183B2N17Ni4S10 formula C63H93BN6Ni2O3S3 fw 1206.84 2609.03 space group P1j P1j A (Å) 15.685(2) 15.8270(7) B (Å) 16.161(2) 16.9597(7) C (Å) 16.750(2) 26.675(2) R (deg) 64.79(1) 100.618(7) β (deg) 72.16(1) 99.450(8) γ (deg) 66.73(1) 92.910(5) V (Å3) 3479.7(6) 6917.7(7) Z 2 2 Dcalcd., (g/cm3) 1.152 1.253 µ (mm-1) 0.675 0.740 R1a (R1 all data) 0.0561 (0.0809) 0.0567 (0.1222) wR2b (wR2 all data) 0.1585 (0.1687) 0.1244 (0.1400) max, min peaks, e-/Å3 1.609/-2.193 0.472/-0.361 a R1 ) Σ| |Fo| - |Fc| |/ Σ|Fo|. b wR2 ) { Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]}1/ 2.
[{NiII2L}2(µ-S6)](BPh4)2 (6 · (BPh4)2). To a solution of [Ni2L(BH4)]ClO4 (90 mg, 0.10 mmol) in acetonitrile (30 mL) was added a solution of elemental sulfur (9.6 mg, 0.30 mmol) in acetonitrile (10 mL). The reaction mixture was stirred for 30 min during which time the color turned from green to yellow-brown. Solid LiClO4 · 3H2O (160 mg, 1.00 mmol) was added. The solution was concentrated to about 7-10 mL. The resulting orange-yellow solid was filtered, washed with cold ethanol, and dried in air. Yield: 62 mg (63% based on [Ni2L(BH4)]ClO4). M.p.: 336-337 °C (decomp.). IR (KBr disk): ν ) 1091 (vs, ν3(ClO4-)), 625 (s, ν4(ClO4-)), 468 (w, ν(SS)), 440 cm-1 (w, ν(SS)). UV/vis(CH3CN): λmax/nm (ε/M-1 cm-1) ) 265 (18038), 304 (13710), 337 (8184), 647 (56), 1102 (72). The tetraphenylborate salt was prepared by salt-metathesis. To a solution of 6 · (ClO4)2 (196 mg, 0.100 mmol) in MeOH was added a solution of NaBPh4 (342 mg, 1.00 mmol) in methanol (10 mL), and the resulting suspension was stirred for 2 h. The solid was filtered, washed with ethanol, and recrystallized from methanol/acetonitrile to give 180 mg (75%) of orange-colored crystals. M.p.: 231-232 °C (decomp.). IR (KBr): ν ) 733 (s, ν(BPh4-)), 704 (s, ν(BPh4-)), 468 (vw, ν(SS)), 445 cm-1 (vw, ν(SS)). UV/vis(CH3CN): λmax/nm (ε/M-1 cm-1): 265 (24962), 273 (22884), 298 (17973), 335 (sh, 10742), 649 (58), 1105 (60). Elemental analysis calcd (%) for C124H168B2N12Ni4S10 (2403.8): C 61.96, H 7.04, N 6.99, S 13.34; found: C 61.71, H 7.23, N 6.69, S 13.09. X-ray Crystallography. Crystals of 4 · BPh4 · MeOH · 2H2O and 6 · (BPh4)2 · 5MeCN were both obtained by slow evaporation of a mixed methanol/acetonitrile solution. Crystal data and collection details are reported in Table 1. The data sets were collected at 213(2) K using a STOE IPDS2T diffractometer. Graphite monochromated Mo KR radiation (λ ) 0.71073 Å) was used throughout. The data were processed with the program STOE X-AREA.61 Structures were solved by Direct Methods and refined by full-matrix least-squares with SHELXL97 on the basis of all data using F2.62 H atoms were placed in calculated positions and treated isotropically using the 1.2-fold Uiso value of the parent atom except the methyl protons, which were assigned the 1.5-fold Uiso value of the parent C atoms. All nonhydrogen atoms were refined anisotropically. In the crystal structure of 4 · BPh4 · MeOH · 2H2O, one t-Bu group was found to be rotationally disordered over two sites. In the crystal structure of (61) X-AREA; Stoe & Cie: Darmstadt, Germany, 2001. (62) Sheldrick, G. M. SHELXL-97 Computer program for crystal structure refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
Hydrosulfide and Hexasulfide Ions Scheme 1. Preparation of Complexes 4 and 6.
6 · (BPh4)2 · 5MeCN, the S62- group is also disordered over two sites. The disorder was modeled by using split atom models to give site occupancies of 0.71(1)/0.29(1) for the two t-Bu group orientations in 4 and 0.92(1)/0.08(1) for the two S62- orientations in 6, respectively. Drawings were produced with Ortep-3 for Windows.63
Results and Discussion Synthesis and Characterization of Compounds. The synthetic procedures are depicted in Scheme 1. Initial attempts aimed at the synthesis of the hydrosulfide complex [Ni2L(SH)]+ (4) followed the method of preparing the hydroxide complex [Ni2L(OH)]+ (2) from [Ni2L(Cl)]+ (1) and (n-Bu4N)OH,27 but surprisingly, 1 proved to be substitutionally inert in reactions with Na2S · 9H2O or (Et4N)SH.64 The reduction of elemental sulfur by the borohydride complex [NiII2L(BH4)]+ (3)38 was sought as an alternative procedure. Indeed, when green 3 · ClO4 was treated with 1 equiv of S powder in CH3CN, a yellow-brown solution forms immediately, and the desired hydrosulfide complex 4 can be isolated from methanol as a brown-yellow ClO4- salt in >70% yields. This reaction presumably involves thioborate/ polysulfide intermediates (as in the LiBH4/S8 system)65,66 which hydrolyze during workup to produce hydrosulfide anions which are trapped by the [NiII2L]2+ fragment. It should be noted that complex 4 is also obtained, in similarly high yields, from reactions in acetonitrile of the extreme labile perchlorato complex [Ni2L(ClO4)]ClO4 (5 · ClO4) with 1 equiv of Na2S · 9H2O, followed by workup from methanol. That polysulfide ions are indeed involved in these transformations was confirmed by the isolation of the hexasulfide complex [{Ni2L}2(µ-S6)](BPh4)2 (6 · (BPh4)2). This material could be reproducibly obtained in yields as high as 70% when elemental sulfur is reacted with 3 · ClO4 in MeCN in a 3:1 molar ratio followed by workup from wet methanol as (63) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (64) Krebs, B.; Bobb, W.; Wellmer, H.-J.; Wiesmann, K. Z. Anorg. Allg. Chem. 1994, 620, 1234–1246. (65) Lalancette, J. M.; Freˆche, A.; Brindle, J. R.; Laliberte´, M. Synthesis 1972, 526–532. (66) Banister, A. J.; Barr, D.; Brooker, A. T; Clegg, W.; Cunnington, M. J.; Doyle, M. J.; Drake, S. R.; Gill, W. R.; Manning, K.; Raithby, P. R.; Snaith, R.; Wade, K.; Wright, D. S. J. Chem. Soc., Chem. Commun 1990, 105–106.
Table 2. Selected UV/Vis Data for Complexes 1-7 complex
coligand
ν2/nm
ν1/nm
∆o/cm-1
ref
Cl658 (41) 998 (67) 10020 27 1a 2a OH655 (52) 1056 (40) 9470 30 3a BH4650 (43) 1074 (77) 9311 38 b 4 SH663 (32) 1175 (49) 8511 this work 5b ClO4578 (129) 1066 (86) 9381 38 6b S62647 (56) 1102 (72) 9074 this work a 7 SPh 667 (52) 1141 (68) 8764 69 a Data refer to the BPh4- salts. b Data refer to the ClO4- salts.
indicated in Scheme 1. At larger (4:1) or smaller (2:1) S/3 ratios a yellow-brown solid of unknown composition precipitates. The complexes 4 and 6 are stable for weeks in the absence of air and protic reagents both in the solid state and in solution. This stability is quite remarkable given that hydrosulfide complexes of sterically less demanding ligands are readily transformed into polysulfides or metal sulfides.43 In the presence of air the yellow-brown color of solutions of 4 and 6 fades away within about 24 h and green products of unknown compositions precipitate. The new compounds gave satisfactory elemental analyses and were characterized byspectroscopicmethods(IR,UV/vis),andX-raycrystallography. The ESI-MS of a freshly prepared acetonitrile solution of 4 shows two nickel-containing fragments at m/z ) 472.68 and 412.68 neither of which is the parent peak. The infrared spectrum of 4 · BPh4 in KBr shows a weak sharp ν(SH) band at 2552 cm-1 typical for complexes with SH- groups.67 For 6 · (BPh4)2 two weak IR bands appeared at 468 and 440 cm-1, attributable to the S-S stretching modes of the S62- unit. These values agree well with those reported for K2S6 and other compounds with a S62- unit.68 Electronic absorption spectra for 4 · ClO4 and 6 · (ClO4)2 were registered in acetonitrile solution in the 250-1600 nm range. The data are collected in Table 2. Absorption data for other [Ni2L(L′)]+ complexes relevant to the present study have been included for comparative purposes. (67) Beck, W.; Danzer, W.; Ho¨ferm, R. Angew. Chem. 1973, 85, 87–88; Angew. Chem., Int. Ed. Engl. 1973, 12, 77-78. (68) Janz, G. J.; Coutts, J. W.; Downey, J. R.; Roduner, E. Inorg. Chem. 1976, 15, 1755–1759.
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Lozan and Kersting Table 3. Selected Bond Lengths (Å) for Complexes 4 and 6 6a
4
Figure 2. UV/vis spectra of 4 · ClO4 (solid line) and 6 · (ClO4)2 (dashed line) in CH3CN at room temperature. Concentrations: ca. 1 × 10-3 M.
Both complexes feature three intense absorption maxima in the UV at ∼270 nm, ∼300 nm, and 330 nm (not shown in Figure 2). These are characteristic for nickel complexes of L2-. The former two can be attributed to π-π* transitions within the aromatic rings of the supporting ligand whereas the latter corresponds to a thiophenolate f NiII charge transfer absorption. Unfortunately, the ligand-to-metal charge transfer (LMCT) bands involving the SH- and S62- groups are not resolved. Above 500 nm complex 4 exhibits two weak absorption bands at 663 and 1175 nm which can be assigned to the spin-allowed 3A2g f 3T1g (ν2) and 3A2g f 3T2g (ν1) transitions of a nickel(II) (S ) 1) ion in Oh symmetry.70 The corresponding values for 6 are significantly blue-shifted to 647 and 1102 nm, respectively. The 3A1g f 3T1g (P) transition (expected below 400 nm) is obscured in each case by the strong LMCT transitions. From the ν1 transition one can obtain rough estimates of the octahedral splitting parameters ∆oct for 4 (≈8511 cm-1) and for 6 (≈9074 cm-1), respectively. Such low values for ∆oct (i.e., ∆oct (4, 6) < ∆oct[Ni(H2O)6]2+ ) 8500 cm-1) are quite typical for N3NiII(µSR)3 chromophores.71 In general, thiolates induce only weak ligand field strengths because of their poor σ-donor bonding abilities. The same is true for the SH- and S62- ligands as indicated by the data in Table 2. 4 and 6 have the lowest ∆oct values. In Table 2 are also included preliminary characterization data for the [NiII2L(µ-SPh)]+ complex 7.69 The ∆oct value for this complex (8764 cm-1) lies between the values of 4 and 6. On the basis of these data, the σ-donor bonding ability of the SR- groups can be ranked as follows: S62- > SPh- > SH-. (69) Preliminary data of the crystal structure determination of 7 · BPh4 · MeCN · EtOH: triclinic, space group P1j, a ) 15.953(3) Å, b ) 16.263(3) Å, c ) 16.398(3) Å, R ) 63.81(3)°, β ) 72.76(3)°, γ ) 66.62(3)° Å, V ) 3465.9(2) Å3, Z ) 2, µ(Mo Ka) ) 0.68 mm-1, R1 ) 0.0523 for 9571 I > 2σI. Complex 7 is of type B. Its preparation and crystal structure will be reported in more detail in a subsequent paper. (70) Lever, A. B. P. Inorganic Electronic Spectroscopy, 2nd edition; Elsevier Science: Amsterdam, 1984. (71) Beissel, T.; Glaser, T.; Kesting, F.; Wieghardt, K.; Nuber, B. Inorg. Chem. 1996, 35, 3936–3947.
5390 Inorganic Chemistry, Vol. 47, No. 12, 2008
Ni(1)-S(3)/S(8) 2.532(1) Ni(1)-N(1) 2.255(3) Ni(1)-N(2) 2.179(3) Ni(1)-N(3) 2.373(3) Ni(1)-S(1) 2.4836(9) Ni(1)-S(2) 2.490(1) Ni(2)-S(3)/S(8) 2.521(1) Ni(2)-N(4) 2.316(4) Ni(2)-N(5) 2.190(3) Ni(2)-N(6) 2.339(3) Ni(2)-S(1) 2.456(1) Ni(2)-S(2) 2.4858(9) Ni-Nb 2.275(4) Ni-Sb 2.495(1) Ni · · · Ni 3.295(1) a Values in square brackets correspond to the b Average values.
2.499(2) [2.494(1)] 2.316(6) [2.211(6)] 2.168(7) [2.171(4)] 2.277(5) [2.378(8)] 2.495(2) [2.538(2)] 2.481(2) [2.506(2)] 2.461(1) [2.460(2)] 2.294(6) [2.250(8)] 2.199(4) [2.177(7)] 2.323(7) [2.378(6)] 2.521(2) [2.501(2)] 2.509(2) [2.509(2)] 2.263(6) [2.261(7)] 2.494(2) [2.501(2)] 3.348(1) [3.364(1)] second [Ni2L]2+ subunit.
Table 4. Selected Bond Angles [deg] in 1, 2, 4, and 6 1, X ) Cl- 2, X ) OH- 4, X ) SHM-X-M 81.02(6) 93.3(3) 81.40(3) M-S-M 81.94(6) 76.96(9) 83.31(3) S-M-S 79.66(6) 82.15(9) 83.55(3) S-M-Xcis 82.54(7) 80.73(2) 79.81(3) N-M-N 87.4(2) 87.9(3) 85.7(1) N-M-Scis 97.09(2) 95.98(2) 94.07(9) N-M-Xcis 93.86(2) 95.05(3) 101.53(9) N-M-Strans 170.33(2) 172.78(2) 172.65(9) N-M-Xtrans 163.8(2) 166.9(2) 177.34(9) a Average values for the two [Ni2L]2+ subunits in 6.
6a, X ) S(3), S(8) 85.21(6) 84.0(6) 82.83(6) 78.09(6) 86.2(3) 93.8(2) 102.9(2) 172.0(2) 171.6
Figure 3. Structure of the hydrosulfide complex 4 in crystals of 4 · BPh4 · MeOH · 2H2O. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted for reasons of clarity. The dashed line indicates a hydrogen bond between the SH moiety and the MeOH solvate molecule (S(3) · · · O(1b) 3.285 Å).
Description of Crystal Structures. The structures of complexes 4 and 6 were further substantiated by X-ray crystallography. Data collection and processing parameters are given in Table 1, selected bond lengths and angles in Tables 3 and 4. The atomic numbering scheme used for the central N3Ni(µ-S)3NiN3 core in 4 was also applied for 6 to facilitate structural comparisons. [Ni2L(SH)]BPh4 · MeOH · 2H2O(4 · BPh4 · MeOH · 2H2O). This structure determination unambiguously confirmed the presence of the cationic hydrosulfide complex [Ni2L(µ-SH)]+ (Figure 3). Although the SH hydrogen atom could not be located from difference Fourier electron density maps, its presence is implied by IR spectroscopy and charge consid-
Hydrosulfide and Hexasulfide Ions
erations (assuming the presence of one dianionic L2-, one BPh4-, one SH-, and two Ni2+ ions). There is also a MeOH solvate molecule that lies in the vicinity of the SH unit (S · · · OMeOH 3.285 Å) indicative of a weak SH · · · OMeOH hydrogen bond.72,73 Unlike in isoelectronic [Ni2L(µ-Cl)]+ (1) or in [Ni2L(µOH)]+ (2), the macrocycle adopts the bowl-shaped conformation B as observed in [Ni2L(µ-ClO4)]+ (see Figure 1 for a schematic representation of the two conformations).35 The presence of the type B conformation of L2- in 4 presumably relates to the larger ionic radii of the SH- group (OH-: 1.19 Å, Cl-: 1.67 Å, SH- 1.93 Å).74 Previous work has shown that the conformation of L2- is coupled to the size of the coligand L′ in the [Ni2L(L′)]+ complexes.29,75 L2- adopts the bowl-shaped conformation when L′ is large, the driving force being the more regular octahedral coordination environment about the Ni2+ ions. Similar arguments can be used to explain the different structures of 1, 2, and 4 (which bear all single-atom bridging ligands). Thus, upon going from the µ-OH complex 2 to the µ-Cl complex 1 the macrocycle maintains conformation A and the deviations of the L-M-L angles from the ideal values increase; particularly affected are the N-M-Xtrans angles. On the other hand, upon going from 2 to the SH complex 4, L changes its conformation and the NiN3S3 polyhedra become more regular. A number of dinuclear nickel complexes with µ-SRgroups have been reported in the literature.76,77 Pohl has reported a dinickel complex with two bridging SH groups.78 As far as we are aware, 4 is the first dinickel complex with a single µ-SH group. The average Ni-SR(thiolate) bond length of 2.479(1) Å in 4 is quite typical for six-coordinate NiII thiolate complexes. For example, the Ni-µ-SPh bonds in the octahedral complexes [Ni(terpy)(µ-SPh)2]2 · 6MeOH79 and [Ni2L(OAc)]BPh480 are 2.465(2) Å and 2.471(1) Å long, respectively. However, the Ni-µ-SH distances in 4 (mean 2.527(1) Å) are significantly longer than the Ni-µ-SR(thiolate) bonds. This is in good agreement with the notion that the SH- ligands are weaker σ-donors than thiophenolates. It should be noted that the Ni · · · Ni distance in 4 at 3.295(1) Å is quite long for complexes containing face-sharing N3Ni(µ-SR)3NiN3 structures. In the trinuclear complexes [{Ni2L′′}2Ni]+ and [{Ni2L′′}2Ni]2+ (L′′ ) octadentate N3S3 ligand), the nickel atoms are separated by only 3.008(2) and (72) Krebs, B. Angew. Chem. 1983, 95, 113–134; Angew. Chem., Int. Ed. Engl. 1983, 22, 113-134. (73) Steiner, T. Angew. Chem. 2002, 114, 50–80; Angew. Chem., Int. Ed. 2002, 41, 48-76. (74) Huheey, J.; Keiter, E.; Keiter, R. Anorganische Chemie, 2 Aufl.;deGruyter: Berlin, 1995; p. 138. (75) Gressenbuch, M.; Kersting, B. Eur. J. Inorg. Chem. 2007, 90–102. (76) Franolic, J. D.; Wang, W. Y.; Millar, M. J. Am. Chem. Soc. 1992, 114, 6587–6588. (77) Silver, A.; Millar, M. J. Chem. Soc., Chem. Commun 1992, 948–949. (78) Pleus, R. J.; Waden, H.; Saak, W.; Haase, D.; Pohl, S. Dalton Trans. 1999, 2601–2610. (79) Baidya, N.; Olmstead, M.; Mascharak, P. K. Inorg. Chem. 1991, 30, 929–937. (80) Journaux, Y.; Glaser, T.; Steinfeld, G.; Lozan, V.; Kersting, B. Dalton Trans. 2006, 1738–1748.
Figure 4. Structure of the [{Ni2L}2(µ-S6)]2+ dication in crystals of 6 · (BPh4)2 · 5MeCN. Thermal ellipsoids are drawn at the 30% probability level. Only one orientation of the disordered S62- unit is displayed. Hydrogen atoms are omitted. Selected bond lengths [Å] and angles [°]: S(3)-S(4) 2.076(2), S(4)-S(5a) 2.037(4), S(5a)-S(6) 2.083(3), S(6)-S(7A) 2.065(2), S(7A)-S(8) 2.063(3); S(3)-S(4)-S(5A) 103.8(1), S(4)-S(5A)-S(6) 107.5(1), S(5A)-S(6)-S(7A) 106.7(1), S(6)-S(7A)-S(8) 104.3(1); S(3)-S(4)-S(5A)-S(6) 76.4, S(4)-S(5A)-S(6)-S(7A) 94.3, S(5A)S(6)-S(7A)-S(8) 83.6.
3.029(1) Å.81 Likewise, for [Ni2L′′′3]2+ (L′′′ ) tridentate N2S ligand) the Ni · · · Ni distance is 3.064(1) Å.82 The Ni-S-Ni angles in these complexes range from 78.9 to 80.16° and are thus more obtuse than in 4 (83.3-81.4°). [{Ni2L}2(S6)] · (BPh4)2 · 5MeCN (6(BPh4)2 · 5MeCN). This salt crystallizes in the triclinic space group P1j. The structure consists of discrete tetranuclear [{Ni2L}2(µ-S6)]2+ dications, tetraphenylborate anions, and acetonitrile solvate molecules. Figure 4 provides an ORTEP view of the structure of 6. Two dinuclear [Ni2L] subunits are linked via a helical S62- chain. Again, both [Ni2L]2+ subunits feature a bowl-shaped conformation for reasons likely to be similar to those detailed above for 4. The average S-S bond length is 2.065(2) Å, and the dihedral S-S-S-S angles range from 76.4 to 94.3°. Similar values are observed in plastic sulfur83 and other S62systems.84–89 (81) Beissel, T.; Birkelbach, F.; Bill, E.; Glaser, T.; Kesting, F.; Krebs, C.; Weyhermu¨ller, T.; Wieghardt, K.; Butzlaff, C.; Trautwein, A. X. J. Am. Chem. Soc. 1996, 118, 12376–12390. (82) Kersting, B.; Siebert, D. Inorg. Chem. 1998, 37, 3820–3828. (83) Greenwood, N. N.; Earnshaw, A. Chemie der Elemente, 1 Aufl.; VCH: Weinheim, 1988; p. 864. (84) Schnock, M.; Bo¨ttcher, P. Z. Naturforsch. 1995, 50b, 721–724. (85) Bacher, A. D.; Mu¨ller, U.; Ruhlandt-Senge, K. Z. Naturforsch. 1992, 47b, 1673–1676. (86) Mu¨ller, A.; Zimmermann, M.; Bo¨gge, H. Angew. Chem. 1986, 98, 259–260; Angew. Chem., Int. Ed. Engl. 1985, 25, 273-274.
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Lozan and Kersting
Figure 5. Temperature dependence of µeff for 4 · BPh4 (open squares) and 6 · (BPh4)2 (open circles). The full lines represent the best theoretical fits to eqs 1 and 2. Experimental and calculated values are provided as Supporting Information.
It should be noted that the Ni-µ-S6 bond lengths in 6 (mean 2.479(2) Å) are significantly shorter than the Ni-µ-SH bonds in 4 averaging 2.527(1) Å, an observation that correlates nicely with the stronger σ-bonding ability of the S62- ion (vide infra). There are no unusual features as far as bond lengths and angles of the [Ni2L]2+ units are concerned. The average Ni-N (2.262(7) Å) and Ni-S (2.498(2) Å) bond lengths in 6 are similar to the values of the compound above. There are no significant intermolecular interactions between the NiII4 complexes within the lattice. The shortest intermolecular Ni · · · Ni distance is at 7.711(1) Å. The present coordination mode of the S62- dianion linking two binuclear N3Ni(µ-SR)3NiN3 cores is also without precedence in the literature. Magnetic Properties of Complexes 4 · BPh4 and 6 · (BPh4)2. Temperature-dependent magnetic susceptibility measurements for 4 · BPh4 and 6 · (BPh4)2 were carried out to establish whether magnetic exchange interactions are present in these complexes. The temperature dependent susceptibility data for dry, powdered samples of the two complexes have been measured between 2.0 and 300.0 K by using a SQUID magnetometer in an applied external magnetic field of 0.5 T. The results are shown in Figure 5 in the form of µeff versus T plots. For 4 · BPh4, the effective magnetic moment (per dinuclear complex) increases from 4.86 µB at 300 K to a maximum value of 5.02 µB at 60 K, and then decreases to 4.15 µB at 2.0 K. Overall, this behavior indicates an intramolecular ferromagnetic exchange interaction between the two NiII ions that leads to an S ) 2 ground-state of the hydrosulfide complex 4. The decrease in µB at low temperatures is indicative of zero-field splitting of NiII. The effective (87) Draganjac, M.; Rauchfuss, T. B. Angew. Chem. 1985, 97, 745–760; Angew. Chem., Int. Ed. Engl. 1985, 24, 742-762. (88) Furuhashi, T.; Kawano, M.; Koide, Y.; Somazawa, R.; Matsumoto, K. Inorg. Chem. 1999, 38, 109–114. (89) Tatsumi, K.; Inoue, Y.; Nakamura, A.; Cramer, R. E.; VanDoorne, W.; Gilje, J. W. Angew. Chem. 1990, 102, 455–457; Angew. Chem., Int. Ed. Engl. 1990, 29, 422-425. Tatsumi, K.; Kawaguchi, H.; Inoue, K.; Tani, K.; Cramer, R. E. Inorg. Chem. 1993, 32, 4317–4323.
5392 Inorganic Chemistry, Vol. 47, No. 12, 2008
magnetic moment of the tetranuclear complex 6 · (BPh4)2 also increases with decreasing temperature, reaching a maximum value of 7.32 µB at 28 K and then decreases again to 6.05 µB at 2.0 K. The value of µB at 28 K is in between a value of 9.84 µB calculated for an ST ) 4 ground-state resulting from the ferromagnetic coupling of four NiII ions (Si ) 1, gi ) 2.20) and a value of 6.22 µB for four noninteracting NiII ions. This behavior indicates the presence of weak ferromagnetic exchange interactions between the NiII ions in the binuclear [Ni2L]2+ entities and negligible coupling across the S62- bridge. The former presumption is in good agreement with the results obtained for 4, while the latter is not surprising in view of the long interdimer Ni · · · Ni distances ranging from 10.689 to 11.218 Å. We tried to simulate the temperature dependence of the magnetic data of complex 4 · BPh4 using the appropriate spinHamiltonian (eq 1)90 which contains a Zeeman and a zerofield splitting term by using a full-matrix diagonalization approach. The introduction of a D parameter is appropriate for octahedral NiII, since the noncubic components of the ligand field may act on the 1A2g ground-state to produce a zero-field splitting which may be of the same order of magnitude as J.91,92 2
H ) -2JS1S2 +
∑ [Di(Sˆiz2 - 31 Si(Si + 1)) + i)1
Siτ] giµBBτˆ
(τ ) x, y, z)(1)
By taking into account the zero-field splitting and a small fraction F (0.035%) of a paramagnetic impurity with S ) 1,93 a good fit of the experimental data, shown in Figure 5 as a solid line, was possible over the full temperature range, yielding J ) +18 cm-1, g ) 2.23, and D ) -82 cm-1. The latter value should be taken as indicative rather than definite, because temperature dependent magnetic susceptibility measurements are not very appropriate for the determination of D.94,95 Nethertheless, J is not influenced markedly by the value of D and represents an accurate measure of the magnetic coupling in this complex. The J and g values determined for 4 · BPh4 are quite typical for dinuclear nickel complexes supported by L2- (e.g., J ) +6.7 cm-1 for [NiII2L(NO2)]+,29 J ) +7.9 cm-1 for [NiII2L(OAc)]+,29 and J ) +27.0 cm-1 for [NiII2L(BH4)]+ 38). The magnetic susceptibility data for 6 · (BPh4)2 were analyzed by the spin-Hamiltonian in eq 2,34 where J1 and J2 represent the intra- and interdimer exchange interactions in tetranuclear 6. The D and g values were considered to be identical for all of the four Ni2+ ions. Notice that D represents an effective zero-field splitting parameter, since the zerofield splitting tensors of all ions are assumed to be colinear. (90) O’Connor, C. J. Prog. Inorg. Chem. 1982, 29, 203–283. (91) Ginsberg, A. P.; Martin, R. L.; Brookes, R. W.; Sherwood, R. C. Inorg. Chem. 1972, 11, 2884–2889. (92) Kahn, O. Molecular Magnetism; VCH: Weinheim, 1993. (93) χ ) χdim(1 - F) + 2χmonoF; χmono ) 2Nag2µB2/3kT. (94) Duggan, D. M.; Barefield, E. K.; Hendrickson, D. N. Inorg. Chem. 1973, 12, 985–991. (95) Meyer, A.; Gleizes, A.; Girerd, J.-J.; Verdaguer, M.; Kahn, O. Inorg. Chem. 1982, 21, 1729–1739.
Hydrosulfide and Hexasulfide Ions
ˆ · Sˆ + Sˆ · Sˆ ) - 2J (S ˆ ˆ ˆ ˆ ˆ ˆ H ) -2J1(S 1 2 3 4 2 1 · S3 + S1 · S4 + S2 · S3 + ˆ ˆ2 - 1 S (S + 1)) + g µ S B ] (τ ) x, y, z) [Di(S S2 · Sˆ4) + iz i B iτ τ 3 i i i)1
for face-sharing bioctahedral NiII2 complexes has not appeared in the literature.
(2)
The main findings of the present work can be summarized as follows: (a) the steric protection-offered by the supporting ligand L2- allows for the preparation and isolation of stable hydrosulfide complexes of labile transition metal ions; (b) the [Ni2L(ΒΗ4)]+ complex reacts rapidly with elemental sulfur and represents a versatile starting material for [Ni2L(µSH)]+; (c) polysulfide complexes such as [{Ni2L}2(µ-S6)]2+ are also accessible from [Ni2L(ΒΗ4)]+ and S8; (d) unlike in [Ni2L(µ-Cl)]+ (1) or in [Ni2L(µ-OH)]+ (2), the larger SHand S62- ions induce the bowl-shaped macrocycle conformation of type B; (e) the SH and S62- ions groups are characterized by their poor σ-donor bonding abilities; (f) 4 and 6 feature wider Ni-S-Ni angles than other N3NiII(SR)3NiIIN3 structures. As a consequence, the orthogonality of the magnetic orbitals is not canceled and ferromagnetic pathways become available to produce a change of the sign of J; (g) magnetic exchange interactions via the hexasulfide moiety in 6 are insignificant. The magnetic properties of complex 6 are solely based on the exchange couplings in the binuclear [Ni2L(SR)]+ subunits.
∑
An excellent fit was obtained yielding J1 ) +23 cm , J2 ) 0 cm-1, g ) 2.12, and D ) -8.5 cm-1. Again, the inclusion of the D parameter improves the low-temperature fit significantly, but it represents by no means an accurate value. Nevertheless, this analysis establishes clearly that magnetic exchange interactions via the hexasulfide moiety are not significant. The magnetic properties of complex 6 are solely based on the exchange couplings in the binuclear [Ni2L(SR)]+ subunits. There are not many examples of compounds reported in the literature which can be compared to the magnetic properties of 4 and 6. The magnetic properties of two relevant linear trinuclear compounds [L′′NiIINiIICoIIIL′′] (8) and [L′′NiIINiIINiIIL′′] (9) containing triply thiophenolato-bridged NiII ions have been reported.80 In complex 8 with a N3NiIIS3NiIIS3CoIIIN3 core a strong intramolecular antiferromagnetic exchange interaction is observed (J ) -61 cm-1). Similarly, for 9, with a central N3NiIIS3NiIIS3NiIIN3 core, the electron spins on adjacent NiII ions couple antiferromagnetically (J ) -28 cm-1). In tris(µ-phenolato)-bridged complexes71,96 or Ni3(acac)6,97 on the other hand, parallel spin alignment occurs. The change of the coupling type from antiferromagnetic in 8 and 9 to ferromagnetic in 4 and 6 may be traced to the widening of the Ni-S-Ni angles (average Ni-S-Ni for 4: 82.7(1)°, 6: 84.4°, 8, 9 < 80°, 71 ). The larger J value determined for 6 would be consistent with this in view. To date, a magneto-structural correlation -1
(96) Elerman, Y.; Kabak, M.; Svoboda, I.; Fuess, H.; Griesar, K.; Haase, W. Z. Naturforsch. 1996, 51b, 1132–1136. (97) Ginsberg, A. P.; Martin, R. L.; Sherwood, R. C. Inorg. Chem. 1968, 7, 932–936. Boyd, P. D. W.; Martin, R. L. J. Chem. Soc., Dalton Trans. 1979, 92–95.
Conclusions
Acknowledgment. Financial support from the Deutsche Forschungsgemeinschaft (Project KE 585/3-1,2,3) and the Universita¨t Leipzig is gratefully acknowledged. We thank Prof. Dr. H. Krautscheid for providing facilities for X-ray crystallographic measurements. Supporting Information Available: X-ray crystallographic data in CIF format. Derivation of the magnetic susceptibility expression for 4 · BPh4 and 6 · (BPh4)2. Experimental and calculated magnetic susceptibility values (PDF). This material is available free of charge via the Internet at http://pubs.acs.org. IC8003432
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